Users should not be allowed to create/remove streams, only consumers

[foxis]

This affects experimental JetStream support.

Currently AddStream and RemoveStream methods of Service will create a stream and remove a stream respectively. This is fine as long as our Brokers allow stream management for regular users. However, in the future, only developers should be able to create streams for their subscriber profiles, and thus configure account limits for JetStream.

Also, since developers should issue users their credentials, developers will be able to set permissions and limits for each user individually.

Right now AddStream creates a stream and a consumer, and RemoveStream will remove the whole stream with all the consumers. This breaks a lot of potential use cases.

The proposed solution:

• AddStream only adds a JetStream consumer to existing stream
• RemoveStream only removes JetStream consumer from an existing stream
• Stream creation with account-wide limits should be done by developer(currently manually using nats cli)